"Judge Hans-Richard Neerforth, who is in charge of the case at the Baden-Baden court systematically obstructs all investigations that would enable German police to track down Doctor Aribert Heim," said Efraim Zuroff, who heads the Wiesenthal Centre in Jerusalem.
"For some reason, Judge Neerforth has opposed several means of verification, as for example tapping the telephone of this criminal's ex-wife," he told AFP on Monday.
"A bank account of this criminal has been found and his family is not touching it, which would suggest its owner is still alive," Zuroff charged.
"Heim is the most wanted Nazi in the world. He has just celebrated his 94th birthday," Zuroff said. "He is a sadist, responsible for the deaths of hundreds of inmates he injected with poison in Buchenwald, Sachsenhausen and Mauthausen," he added, referring to three notorious concentration camps where Heim is suspected of carrying out deadly medical experiments on prisoners.
But the court in Baden-Baden said that the accusations that the judge was impeding the investigations were "groundless."
"Since 2005 alone, the criminal division ... has made 11 international requests for legal assistance to states within and outside Europe, which shows that great efforts are being made in this investigation," a statement said.
It said that the court had to ensure that investigative methods were legal, even in the case of such serious crimes, and that there was only one occasion when it had rejected their use.